I'm aware. They're stand alone updates that mostly people who bought the original game are buying again with new characters, character differences, and different modes. SFIV itself is referred to as a series of games by Capcom and are counted separately. The most important thing to note is that a SFIV player can't play against someone playing Super SFIV or Ultra online.
That's not the usual thing. MK and MKX have the same playerbase so does SF 5 and SF 5 AE.